During the process of assembling or “making-up” a train consist, railcars are run into and collide with each other to couple them together. Since time is money, the speed at which the railcars are coupled has significantly increased. Moreover, and because of their increased capacity, railcars are heavier than before. These two factors and others have resulted in increased damages to the railcars when they collide and, frequently, to the lading carried within such railcars.
As railroad car designer/builders have reduced the weight of their designs, they have also identified a need to protect the integrity of the railcar due to excessive longitudinal loads being placed thereon, especially as the railcars are coupled to each other. Whereas, such longitudinal loads frequently exceed the design loads set by the AAR. Providing a coupling system at opposed ends of each railcar has long been known in the art. Such a system typically includes a draft assembly comprised of a coupler for releasably attaching two railcars to each other and a an energy management or cushioning assembly arranged in operable combination with each coupler for receiving and dissipating external forces experienced by the coupler during make-up of the train consist and during in-service operation of the railcar.
In-service train action events and impacts occurring during the “make-up” of a train consist subject the draft assembly at opposed ends of the railcars to buff impacts, while in-service train action events subject the draft assembly to draft impacts. The impacts associated with these events are transmitted from the couplers to the respective energy management or cushioning assembly and, ultimately, to the railcar body. That is, as the couplers are pushed or pulled, be it during in-service operations and/or during the “make-up” of a train consist, such movements, although muted to some degree by the cushioning assembly, are translated to the railcar body.
Typically, draft assemblies further include a yoke that is operably coupled to the coupler as through a pin or key, a follower, and the cushioning assembly. Generally, the follower is positioned against or arranged closely adjacent to the butt or rear end of a shank portion on the coupler in the draft pocket and within confines defined by the yoke. The cushioning assembly is positioned between the follower and rear stops on the draft sill.
In buff events, the rear or butt end of the coupler moves axially inward against the follower and toward rear stops on the draft sill. As the coupler and follower move rearward, a portion of the shock or impact event is absorbed and dissipated by the cushioning assembly.
In draft events, slack between adjacent railcars is taken up beginning at the end of the train and ending at the other end of the train. As a result of the slack being progressively taken up, the speed difference between the railcars increases as the slack inherent with each coupling system at each end of the railcar in the train consist is taken up, with the resultant increase in buff and draft impacts on the coupling system. For example, when a locomotive on a train consist of railcars initially begins to move from a stopped or at rest position, there may be 100 inches of slack between the 50 pairs of coupling systems. This slack is taken up progressively by each pair of joined coupling systems in the train consist. After the slack in the coupling system joining the last railcar to the train consist is taken up, the next to the last railcar may be moving at 4 miles per hour. Given the above, it will be appreciated, the slack in the coupling system of those railcars closest to the locomotive is taken up very rapidly and those two railcars closest to the locomotive are subjected to a very large impact event being placed thereon. Such large impact events are capable of damaging the lading in the railcars.
Moreover, most of today's railcars use and embody air brakes. Such air brakes require an air hose to extend between railcars. While bridging the distance between adjacent railcars, the length of such air hoses is limited unless two or more air hoses are coupled to each other whereby adding to the overall cost. Of course, if the distance between the railcars exceeds the length of the air hose, the air hoses will separate from each other thereby affecting control over the braking function. Accordingly, there is a need to limit coupler travel in draft whereby limiting the distance between railcars during in-service operation of the train consist.
Thus, there is a continuing need and desire for a railcar coupling system which is capable of limiting the travel of the system during operation of the railcar in both buff and draft directions.